The development of computer tomography goes on the one hand towards systems with multi X-ray tubes and multi-slice cone beam detectors especially in order to obtain three-dimensional projection data sets of a patient which are suitable for a three-dimensional reconstruction of the scanned volume.
On the other hand, computer tomography is further developed for new applications and especially improved imaging qualities, wherein especially the energy information of the X-ray beam (“spectral CT”) is used as additional physical information to improve such image quality and contrast resolution and also to enable new diagnostic benefits like material identification and quantification from the clinical images.
Both these applications and developments require power supplies which generate two or more, preferably different high output voltages for at least one X-ray tube. Furthermore, it is desired especially for spectral CT imaging to switch between at least two different X-ray tube voltages (or voltage levels) very fast, because otherwise severe motion artifacts are to be observed.
A particular problem with known such high voltage generators for two independent high voltages is that they require much space and are comparatively heavy so that they are not well suited for use in a rotating gantry of a computer tomography apparatus.
Another problem is that a high voltage which is generated with a voltage multiplier usually cannot be changed or varied within a sufficiently short time which is necessary for obtaining spectral X-ray images of sufficient quality. This applies as well for a multi-phase high voltage multiplier as disclosed in WO 2003/049270 A2.